1. Field of Invention
The present disclosure of invention relates to flat panel displays, and more particularly, to liquid crystal displays (LCD's) in which each pixel unit is divided into a main pixel area and a subsidiary pixel area and the pixel-electrodes of these divided areas are to be charged to different potentials during a same horizontal line period.
2. Description of the Related Art
A liquid crystal display (LCD), which is one of a variety of different kinds of flat panel displays, is a device that forms an image by adjusting a transmitted amount of light supplied from a light source by using the optical anisotropy property of liquid crystal molecules and the polarization characteristics of a polarizer to control light transmitivity through each of color-filter covered pixel units. The process of controlling the orientation of the liquid crystal molecules includes charging one or more electrodes (pixel-electrodes) to a desired electrical potential. In recent years, use of liquid crystal displays has been increasingly widening because it has various features such as being lightweight, compact, offering high resolution, large screen sizes, and low power consumption.
However the conventional liquid crystal display (e.g., the kind with just one pixel-electrode per pixel unit) suffers from the drawback of having a relatively narrower viewing angle than that of other kinds of displays because it forms an image by using the light transmitted only along a main transmission axis of liquid crystal molecules in a main area of each pixel unit. Thus, in order to widen the viewing angle, various techniques have been proposed. One of the proposed techniques is referred to as the Super Patterned Vertical Alignment (SPVA) scheme. According to the SPVA scheme, the total area of each pixel unit is divided into a main pixel area (having a respective main pixel-electrode) and one or more subsidiary pixel areas (having respective subsidiary pixel-electrodes). The pixel-electrodes of the so divided pixel unit are often independently driven to respectively different charge potentials so as to create an electric field gradient within the pixel unit and thus orient the liquid crystal molecules therein along more than just one main axis. Accordingly, different charging voltages need to be applied to the divided electrode areas of the pixel unit so that the light transmission axes of the liquid crystal molecules in the pixel unit are oriented along various angles, so that the viewing angle of a given image can then be improved, and in particular, so that side visibility can be improved. In the conventional SPVA scheme, each pixel unit is generally connected to and driven by two independent gate lines and one data line (this is referred to as a 2G-1D cell structure).
However, when compared to the more conventional 1G-1D cell structure, the SPVA scheme suffers the drawback that it has more independent pixel-electrodes in need of independent charging than does the general scheme, and accordingly, it is difficult to suitably provide sufficient charging time of each independent electrode inside the pixel unit, particularly if the to-be-charged, total capacitance associated with the one or more subsidiary pixel areas is substantially greater than the to-be-charged, total capacitance associated with the main pixel area. For example, in a case where one pixel unit is divided into a single subsidiary pixel area (hereafter also “sub pixel”) and a smaller main pixel area (hereafter also “main pixel”, the charging time available for each subdivision of such a pixel unit is often reduced to a half (e.g., ½ of horizontal scan time 1H) of what is available to a conventional 1G-1D cell structure. As mentioned, it is often desirable that the subsidiary pixel and the main pixel are charged with data signals having different potentials respectively. However, when the charging times of the data signals are controlled to be equal (e.g., each getting just ½ of H), the respective main and subsidiary pixel electrodes may be undercharged or overcharged relative to the desired potentials for the respective main and subsidiary pixel electrodes. As a result of such insufficient charging time, the display quality such as side visibility and color impression may be one that is below expectation. Incidentally, the terms, subsidiary and main as used herein do not necessarily apply to optical importance of the respective pixel parts. Instead, for one subset of embodiments, the term subsidiary implies that this electrode will generally receive a data signal of relatively lower or subsidiary absolute magnitude (L-DATA) while the main part will receive a data signal of relatively higher or more absolute magnitude (H-DATA). Of course, for another subset of embodiments this fixed interrelation between applied data signals does not apply and then the terms, subsidiary and main become arbitrary designations rather than of any significant meaning.